<html>
    <head>
      <base href="https://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - Unitialized variable usage not checked in some cases"
   href="https://llvm.org/bugs/show_bug.cgi?id=26640">26640</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Unitialized variable usage not checked in some cases
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>3.8
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>FreeBSD
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Driver
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>bdrewery@FreeBSD.org
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>cat > test.c << EOF
#include <stdlib.h>

int main() {
  char *p;
  int maybe_set_p = 0, flag = 1;

  if (maybe_set_p)
    p = (char*)malloc(1);

  if (flag && p)
    ;

  return 0;
}
EOF
clang38 -Wall -o test test.c

No warning is given about the uninitialized use of p in 'if (flag && p)'.

Changing the 'if (maybe_set_p)' to 'if (0)' shows the warning:

example.c:10:15: warning: variable 'p' is uninitialized when used here
[-Wuninitialized]
  if (flag && p)
              ^
example.c:4:10: note: initialize the variable 'p' to silence this warning
  char *p;
         ^
          = NULL
2 warnings generated.</pre>
        </div>
      </p>
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